Nano drug carriers can achieve the passive targeting to the tumor tissues by the high permeability and retention (EPR) effect on tumor tissues, which greatly improves the drug utilization and reduces the toxicity and side effects of the free drugs on the normal tissues. Polymeric micelles, as drug carriers, have the advantages of solubilizing hydrophobic drugs, improving drug stability and sustained-release drugs.
In order to achieve the goal of targeting drug release to the tumor tissue, there are many reports on biodegradable carriers with environmental intelligent responsiveness (such as pH, reduction potential, enzyme and so on). In recent years, some researchers focus on environmental intelligent responsive hyperbranched polymers. It is found that the hyperbranched polymers have novel structures and unique properties such as high solubility, low viscosity, three-dimensional interior cavity spherical structures and so on. A large number of cavities in the structure can be used for hydrophobic drug loading. The drug loading is improved during the process. Hyperbranched polymers can be degraded into non-toxic small molecules and release drugs by acidic or reductive stimulations of the tumor cell environment.
However, in literatures the reported synthetic methods for preparation of environmental responsive hyperbranched polymers usually take many steps, and a lot of organic solvents are needed in the preparations, which limits the applications in biomedical fields. At the same time, most of the hyperbranched polymer micelles currently reported do not exhibit reductive responsiveness and are inevitably retained in vivo.